This app uses Yahoo Pipes to grab your Dopplr feed which it uses to get the location points. These are sent to Geonames database to gather elevations via a DEM query. That data is sent here in JSON form and then handed off to the Google Visualization API 3.
This app was built by bryan boyer, a trained architect who used to build web apps (and sometimes still does).
1. This is going to be something with a nasty hash at the end.
2. The math does not take in to account duration of time spent in each location.
3. The visualization API is nice but its level of customization is pitiful. I can't even specify the min/max of the graph? Come on?!